Resolvers are commonly used in commercial, industrial, and military systems to obtain an estimate of the position to which the device is attached. A typical electrical resolver unit includes two stationary outer windings placed at ninety degree angles around an inner rotating winding which is coupled to the shaft of a rotating machine element. An excitation signal is applied to the rotating winding so that as the shaft rotates, a varying voltage is induced in the stationary windings. Because the stationary windings are ninety degrees apart, they will produce a sine and cosine variant of the excitation signal. By measuring the output sine and cosine signals in relation to the input excitation signal, a monitoring controller is able to determine the angular position of the shaft.
Under many of the control techniques applied to these devices, a velocity control objective is often achieved through some combination of differentiation, filtering, and estimation techniques. Such techniques often are unable to distinguish true position movement from reported position movement from the resolver which can lead to errors in the estimated velocity. As the performance requirements of the velocity control loop increase, the velocity-estimate errors lead to undesirable system performance. Such undesirable performance often includes the presence of electrical current ripple being generated in an electrical machine controlling the movement of the resolver.
In order to extend the performance range of such systems, it is possible to correct for the resolver signal errors which lead to the velocity estimate ripple. Past techniques have either not corrected for a sufficient portion of the resolver errors to meet all stringent performance requirements, have presented techniques which do not adaptively drive the error signals to zero, require additional computation power beyond the disclosed technique, or do not utilize the error information in the same fashion as the technique presented herein.